/Engine/Plugins/Runtime/Metasound/Source/MetasoundFrontend/Public/MetasoundFrontendController.h
Returns the variable mutator node. If none exist, one is created.
[FNodeHandle](API\Plugins\MetasoundFrontend\FNodeHandle) FindOrAddVariableMutatorNode ( const [FGuid](API\Runtime\Core\Misc\FGuid) & InVariableID )